1. Field of the Invention
The present invention relates generally to remote control devices, and more particularly to radio frequency transmitters for remote control of garage door openers, and still more particularly to a universal transmitter for a garage door opener.
2. Description of the Prior Art
Remote control of garage door openers has become common, with numerous manufactures supplying a variety of devices. For security purposes, separate carrier frequencies and a plurality of modulation codes are used for each manufactured product line. The many variables necessary for security makes manufacture expensive, and especially for smaller distributors, makes parts stock a burden.
Efforts have been made to increase the number of receivers a transmitter can accommodate, as in Drori et al. U.S. Pat. No. 4,890,108 wherein the manufacturer stores predetermined modulation codes, which can be recalled by the user. This is accomplished through the addition of an EEPROM in cooperation with the usual microprocessor. The invention does not allow for user programming of modulation format or for adjustment of the carrier frequency. Methods whereby the user code can be programmed by the owner are also disclosed in Liotine et al. U.S. Pat. No. 4,529,980.
In summary, the prior art deals primarily with user code flexibility and ease of operation, rather than with a universal transmitter having capability for selectably varying the carrier frequency. These devices have increased the number of different transmitters on the market, but have not realized a universal transmitter compatible with most garage door opener receivers.